Mitch:

IPC-SM-782A does contain the land pattern formulas. Look on pages 10-14 
of the document. 

The Surface Mount Land Patterns Subcommittee, which is responsible for 
IPC-SM-782 and its updates, has acknowledged that there are some typos in 
the document, which may explain the "inconsistencies." Nevertheless, one 
must also consider three factors when comparing IPC-SM-782 to 
its successor:

1. Land patterns in the "A" rev. were developed which the goal of the best 
possible solder joint per J-STD-001, which was released in April 1992 
(well after the 1987 release of IPC-SM-782).

2. Manufacturing tolerances change as improved equipment reaches the 
marketplace. These, too, will impact the land patterns.

3. The land patterns in the second half of the document reflect the 
industry consensus based on empirical knowledge. Given the variety of 
manufacturing methods in use, some tinkering of the land patterns will 
probably be necessary from time to time.

An amendment to IPC-SM-782A is underway. IPC awaits the final draft from 
the aforementioned volunteer committee. Per ANSI rules, we will then 
circulate (30 days) the proposed amendment to our full membership for 
approval. If all votes are affirmative, IPC will publish the amendment.
Unfortunately, it is difficult at this time to predict when it will be ready.

We welcome your inputs.

Mike Buetow
IPC Technical Staff
2215 Sanders Road
Northbrook, IL 60062-6135
T: 708-509-9700
F: 708-509-9798
[log in to unmask]



On Fri, 8 Dec 1995, Mitch S. Morey wrote:

> I would like to recommend the creation of the IPCsm782 Designer's Council.
> There seems to be alot of inconsistancies with the latest (A) rev to the
> IPC-SM-782 (surface mount land patterns) standard.
> 
> For one,  the land pattern equations no linger reside in the spec, like the
> previous release had.  What equations were used to develop these land
> patterns.  The land patterns deviate SO MUCH from the previous release
> that we (TRW) has resisted using the 782A standards until we can establish
> whether these values are valid!
> 
> I would like to hear more from anyone who has decided to use the Rev A
> release.
> 
> Thank you,
> 
> Mitch Morey
> Sr. PCB Designer
> TRW, Inc.
> Redondo Beach, CA
> (310) 814-5765
> Fax: (310) 812-4949
> ([log in to unmask])
> 
>